Persons acquainted with the operation of upwardly acting doors having an electrical operator for effecting door movement are aware that some door operators have a safety switch whereby the direction of door movement is automatically reversed if the door engages an obstruction during movement in its downward or closing direction. This safety feature, as disclosed in U.S. Pat. No. 3,474,317 owned by the assignee of this application, has been provided to prevent damage to equipment and injury to personnel which might result from continued operation of the door. While operators of this type have been commercially acceptable, nevertheless they do possess structural and operational features whih have been undesirable either from a cost, maintenance or operational view point.
To improve upon operators of this type, U.S. Pat. No. 3,764,875, also owned by the Asignee of this application, discloses an operator having a mechanical override system for deactivating the safety switch when the door is within a preselected distance from either its fully opened or fully closed position to prevent reversal of the door movement. While the operator of this patent does possess the ability to deactivate the safety switch, nevertheless, this operator is structurally complex and does not possess the degree of flexibility necessary to provide for optimum control over all of the door movements.
Accordingly, copending application Ser. No. 557,929, filed Mar. 13, 1975, discloses therein a door operator having improved switch mechanism and circuitry capable of overcoming the problems and achieving the results set forth above. In particular, the control system of this operator is highly desirable with respect to the manner in which it controls the door movement when the door approaches its fully opened and fully closed positions. However, the safety or reversing switch associated with this operator is of a type which is designed primarily for use with a chain drive, and thus does not possess the optimum structural and operational characteristics for use with a door operator employing a screw drive.
Since the present invention relates to an improved door operator which utilizes a screw drive, namely an elongated drive screw for driving a carriage which is interconnected to the door, the present invention thus relates to an improved safety or reversing mechanism disposed for association with the operator to cause reversing of the door movement when the door strikes an obstruction while moving in the closing direction.
Door operators employing an elongated drive screw for controlling the opening and closing of the door are also well known, and one such operator is disclosed in U.S. Pat. No. 2,882,045. The operator of this patent employs an elongated drive screw which controls a slidable carriage, which carriage is interconnected to the door. In addition, a floatable or slidable bearing assembly is associated with the carriage and the screw to provide for additional support for the screw during movement of the carriage therealong. However, the operator of this patent has the screw resiliently urged into a central axial position, with the screw being axially movable in either direction away from this position for either stopping the door or reversing the direction thereof. In this operator, the safety or reversing switch cooperates directly with this screw to cause reversing of the door movement when the closing door strikes an obstruction. However, this direct association between the screw and the switch makes adjustment of the reversing action difficult. Also, the sensitivity of the reversing mechanism is seriously effected by the floatable mounting which permits the screw to be axially displaced in opposite directions. The direct coaction between the screw and safety switch also makes it difficult to create a sufficient force on the screw by use of a simple and compact structure so as to result in activation of the reversing mechanism at the desired force level.
The door operator of U.S. Pat. No. 2,882,045 also relies upon the opposite axial displacement of the screw for activating the limit switches which control the end positions of the door. Thus, the limit switches which control the end positions of the door, and the limit switch which controls the reversing of the door, are thus all dependent upon the same axial displacement of the screw. Independent control and adjustment of the various switch actuating functions is accordingly difficult to achieve, and thus the control functions are not always carried out under the optimum conditions relative to one another. In addition, maintaining the screw in a central axial position is particularly difficult since the weight of the door imposes a force on the screw in the same direction as the drive motor when the door is travelling downwardly, whereas the weight of the door imposes a force on the screw which is opposite to the drive force when the door is moving upwardly. This unbalance of forces on the screw thus makes maintaining of the screw in its central axial position, which position is maintained by springs, extremely difficult. The difficulty of maintaining the screw in this spring-urged central position also effects the other limit switches which control the door movement.
Accordingly, the present invention relates to a door operator which employs a drive screw for controlling the door movement, which door operator overcomes the disadvantages associated with the screw-type door operator mentioned above. In addition, the present invention provides an improved reversing mechanism adapted to coact with the door operator, particularly the screw, for permitting reversing of the door movement, which reversing mechanism is particularly suitable for use with the remainder of the control system disclosed in the above-mentioned application Ser. No. 557,929.
It is also an object of the invention to provide an improved operator, as aforesaid, wherein the safety or reversing mechanism is actuated in response to axial movement of the drive screw, with the axial movement of the drive screw functioning solely to control the reversing mechanism whereby the limit switches for controlling the end positions of the door are independent of this axial movement.
The objects of this invention, as aforesaid, are additionally accomplished by mounting the drive screw of the operator so that it is normally maintained in a preselected position, which screw is movable solely in one direction away from this position for controlling the reversing mechanism, whereby a more precise control over the screw movement is possible, while at the time permitting the door operator and particularly the drive screw and the mounting therefor to be of maximum structural and operational simplicity.
Other objects and purposes of the invention will be apparent to persons familiar with this type of equipment upon reading the following specification and inspecting the accompanying drawings.